Dynamic range is the ratio between the largest and smallest possible signals a sensor can generate. As used herein, the term “dynamic range” refers to the dynamic range of a digital imaging device, such as a digital camera.
The dynamic range of a digital camera can be defined as the ratio of the maximum measurable light intensity to the minimum measurable light intensity, and is usually measured in a base-2 logarithmic value, or “stop,” which describes the total light range by powers of 2. For example, a contrast ratio of 1024:1 (or 210:1) could therefore be described as having a dynamic range of 10 stops. Each unit stop, or power of an exposure step, may be described as one unit of an exposure value (e.g., 1 EV).
A drawback of typical digital cameras may be the capacity to reproduce an image scene with high dynamic illumination range, or high contrast. In many instances, the dynamic illumination range of a digital imaging device is limited by the sensor technology and/or parameter settings of the digital camera. For example, automatic settings of conventional cameras can result in images that are over or under exposed. Accordingly, attempts have been made to increase the dynamic range of imaging devices.
One conventional approach attempts to increase the dynamic range of an imaging device by capturing many images of a scene. Further, these images are usually captured with the same settings. However, with hand-held digital cameras, the number of images captured for generating a high dynamic range of a scene should be minimized in order to minimize various artifacts that can be introduced to scene data. These artifacts may result from local motion within the scene and/or global motion, such as camera shake, between the camera and the scene. Global motion may be addressed by supporting the imaging device, for example using a tripod. However, a fixed support does not address the effects of local motion. Further, this approach and other conventional approaches do not address determining exposure parameters for image capture, as conventional enhancements are typically performed during post processing.
Another conventional approach involves the use of specialized sensors to capture a single image frame with varying parameters of the sensor. The conventional methods and devices based on these sensors, however, typically result in image data with reduced resolution as detected image data is captured with a single sensor reducing the detail of captured data. These sensors may further be disadvantageous due to cost involved to provide the specialized sensors. Other conventional approaches relying on post-processing of image data similarly fail to address providing HDR image detection for users of portable imaging devices such as digital cameras.
Accordingly, there is a need in the art for high dynamic range (HDR) imaging devices which overcome one or more of the aforementioned drawbacks.